Chemical-mechanical polishing (“CMP”) processes are used in the manufacturing of microelectronic devices to form flat surfaces on semiconductor wafers, field emission displays, and many other microelectronic substrates. For example, the manufacture of semiconductor devices generally involves the formation of various process layers, selective removal or patterning of portions of those layers, and deposition of yet additional process layers above the surface of a semiconducting substrate to form a semiconductor wafer. The process layers can include, by way of example, insulation layers, gate oxide layers, conductive layers, and layers of metal or glass, etc. It is generally desirable in certain steps of the wafer process that the uppermost surface of the process layers be planar, i.e., flat, for the deposition of subsequent layers. CMP is used to planarize process layers wherein a deposited material, such as a conductive or insulating material, is polished to planarize the wafer for subsequent process steps.
In a typical CMP process, a wafer is mounted upside down on a carrier in a CMP tool. A force pushes the carrier and the wafer downward toward a polishing pad. The carrier and the wafer are rotated above the rotating polishing pad on the CMP tool's polishing table. A polishing composition (also referred to as a polishing slurry) generally is introduced between the rotating wafer and the rotating polishing pad during the polishing process. The polishing composition typically contains a chemical that interacts with or dissolves portions of the uppermost wafer layer(s) and an abrasive material that physically removes portions of the layer(s). The wafer and the polishing pad can be rotated in the same direction or in opposite directions, whichever is desirable for the particular polishing process being carried out. The carrier also can oscillate across the polishing pad on the polishing table.
In polishing the surface of a substrate, it is often advantageous to monitor the polishing process in situ. One method of monitoring the polishing process in situ involves the use of a polishing pad having an aperture or window. The aperture or window provides a portal through which light can pass to allow the inspection of the substrate surface during the polishing process. Polishing pads having apertures and windows are known and have been used to polish substrates, such as semiconductor devices. For example, U.S. Pat. No. 5,893,796 discloses removing a portion of a polishing pad to provide an aperture and placing a transparent polyurethane or quartz plug in the aperture to provide a transparent window. The transparent plug can be integrally molded into the polishing pad by (1) pouring liquid polyurethane into the aperture of the polishing pad and subsequently curing the liquid polyurethane to form a plug, or by (2) placing a preformed polyurethane plug into the molten polishing pad material and then curing the entire assembly. Alternatively, the transparent plug can be affixed in the aperture of the polishing pad through the use of an adhesive followed by curing of the adhesive over several days. Similarly, U.S. Pat. No. 5,605,760 provides a pad having a transparent window formed from a solid, uniform polymer material that is cast as a rod or plug. The transparent plug can either be inserted into the aperture of an opaque polymeric polishing pad while the pad is still molten in a mold, or the window portion can be inserted into the aperture of a polishing pad using an adhesive.
Such prior art methods for affixing a window portion into a polishing pad have many disadvantages. For example, the use of adhesives is problematic insofar as the adhesives can have harsh fumes associated with them and often require curing over 24 hours or more. The adhesive in such polishing pad windows also can be subject to chemical attack from the components of the polishing composition and so the type of adhesive used in attaching the window to the pad has to be selected on the basis of what type of polishing system will be used. Furthermore, the bonding of the window portion to the polishing pad is sometimes imperfect or degrades over time such that leakage of the polishing composition between the pad and the window occurs. In some instances, the window portion can even become dislodged from the polishing pad over time.
The aforementioned problems can be overcome through the use of a one-piece polishing pad, in which either the entire polishing pad is transparent or the transparent window portion is prepared by specially modifying a small portion of an opaque polishing pad. For example, U.S. Pat. No. 6,171,181 discloses a polishing pad comprising a window portion that is a one-piece article formed by rapidly cooling a small section of the polishing pad mold to form a transparent amorphous material that is surrounded by a more crystalline and thus opaque polymer material. However, such a manufacturing method is costly, is limited to polishing pads that can be formed using a mold, and necessitates that the polishing pad material and the window material have the same polymer composition.
Thus, there remains a need for a method of producing polishing pads with optically transmissive regions that can be applied to a wide variety of polishing pad and window materials, which can form a stable, integral bond between the window and the pad that is not prone to leakage, and can be produced without sacrificing time- and cost-efficiency.
The invention provides such a method of producing polishing pads comprising optically transmissive regions. These and other advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.